Adsorption Of Phthalic Acid Esters On Clay Minerals And Soils

Phthalic acid esters ?PAEs? are widely used as plasticizers and easy to be released into the environment, and subsequently accumulated in soils, which post potential harm to human and environment. PAEs have estrogen-like effect, cause reproductive function decline and hypoimmunity to various creatures, including humans. It has serious inplications for hunman health and reproduction. Clay mineral is an important component of soil, has important effect on organic pollutants migration. Therefore, this article research adsorption behavior of PAEs to clay minerals and soils from the following three aspects:1.First, when PAEs adsorbed onto soil, clay mineral would inevitably affect the transformation processes of PAEs, and these transformation processes could determine the fate of PAEs in the soils. In order to understand the adsorption of PAEs to the clay minerals, we have chosen two montmorillonite clays ?FZ-10, SMF? and one kaolinite clay ?Kao? as the adsorbents that saturated with 0.5 M KC1 solution ?K-FZ-10, K-SMF and K-Kao?. The results showed that the adsorption of PAEs to clay minerals were in the following orders: dimethyl phthalate ?DMP?< diethyl phthalate ester ?DEP?< di-n-butyl phthalate ?DnBP?, and their adsorption coefficient values ?Kd? were positively related to their hydrophobicities ?DMP< DEP< DnBP?, and the adsorption capacity of clay minerals was increasing with the increased hydrophobicities of PAEs. The adsorption of DEP to three clay minerals was in the following:K-FZ-10> K-SMF> K-Kao, both the type and surface area of clay minerals contributed to the adsorption ability. Based on the results of adsorption isotherms conducted at different temperature ?4??10??20? and 30??, the adsorptions of three PAEs to K-FZ-10, K-SMF and K-Kao were decreased with temperature increasing, which indicated that the adsorption was exothermic and spontaneous. This study revealed that the type of clays, hydrophobicity of PAEs and temperature were three important factors that affected the adsorption of PAEs to clay minerals. The greater the surface area of clay minerals, the more hydrophobic of PAEs, the lower environment temperature, the greater the adsorption quantity of PAEs.2. Secondly, in order to explore the adsorption mechanism of PAEs in clay minerals, batch adsorption experiments were conducted to investigate the environmental effects on the of diethyl phthalate ester ?DEP? to K-/Na-/Ca-mont clay minerals. The results showed that DEP adsorption isotherms were well fitted with the Freundlich model; there was no significant effect of pH and ionic strength on DEP adsorption to K-mont/Ca-mont. but to Na-mont clay. Based on X-ray diffraction and FTIR spectra, DEP molecules could intercalate into K-/Ca-mont interlayer, and might interact with clay through H-bonding between carbonyl groups and clay adsorbed water. Coated humic acid on clay surface would enhance DEP adsorption to K-mont clay at low concentration?eg. Ce< 0.26 mM?, but not at high concentration. Based on adsorption isotherms at varied temperatures, indicated that the adsorption was exothermic and spontaneous.3.In order to research the adsorption behavior of PAEs in natural soil, we choosed four different depth ?0-20 cm,20-40 cm? of Chinese typical soil ?black soil, red soil, paddy soil and fluvo-agvic soil? as the adsorbents. Batch adsorption experiments were conducted to study the migration behavior of PAEs in soils. The results showed that the soil adsorption of DEP was affected by soil organic matter, the adsorption of DEP to soil was below 2 mmol·kg^-1. The adsorption capacity of DEP to different depth of soil was followed as:black soil ?0-20 cm?> black soil ?20-40 cm?? fluvo-agvic soil ?20-40 cm?> paddy soil ?0-20 cm?> fluvo-agvic soil ?0-20 cm?? rice soil ?20-40 cm?> red soil ?0-20 cm??red soil ?20-40 cm?. In the process of surface black soil and red soil adsorption, with the increasing of solution concentration of DEP, DOC concentration increased significantly. The results showed that the dissolved organic matter of soil has important influence migration hvdrophobic organic compounds in soil.